A substrate processing apparatus performs a certain plasma process on a semiconductor wafer (hereinafter, referred to as simply a “wafer”) serving as a substrate by using plasma. The substrate processing apparatus includes a depressurized processing chamber; a mounting table provided in the processing chamber; a HF (High Frequency) high frequency power supply configured to be connected to the mounting table and apply a high frequency voltage of a relatively high frequency (hereinafter, referred to as a “HF high frequency voltage”) to a susceptor serving as the mounting table; and a LF (Low Frequency) high frequency power supply configured to be connected to the susceptor and apply a high frequency voltage of a relatively low frequency (hereinafter, referred to as a “LF high frequency voltage”) to the susceptor.
A processing gas introduced into the processing chamber is excited into plasma by applying the HF high frequency voltage. A bias voltage is generated in the susceptor by applying the LF high frequency voltage. In this case, a self bias is generated in the susceptor. When an electric potential of the susceptor is time-averaged, the electric potential has a negative value. Accordingly, ions are attracted to the susceptor by the electric potential difference.
However, since the LF high frequency voltage is a sine wave, it is known that in the case where the bias voltage is generated in the susceptor by applying the LF high frequency voltage, an energy distribution of ions attracted to the susceptor has a peak value of relatively low energy and a peak value of relatively high energy, and further, has a certain range as shown in FIG. 9. (see, for example, Patent Document 1)
Patent Document 1: Japanese Patent Laid-Open Application No. 2009-187975 (FIG. 14)
However, etching by ions of relatively low energy is strongly isotropic. Etching by ions of relatively high energy is strongly anisotropic. Accordingly, if a bias voltage is generated in a susceptor by applying the LF high frequency voltage, anisotropy in etching becomes strong even when isotropy in the etching is needed. Also, isotropy in etching becomes strong even when anisotropy in the etching is needed. As a result, a desired shape of a hole or a trench may not be formed by the etching. That is, when the bias voltage is generated in the susceptor by using the LF high frequency voltage, processing controllability in an etching process is not so good.
The present illustrative embodiments provide a substrate processing apparatus capable of improving the processing controllability in the etching process.